The announcement of abnormal road traffic conditions, such as a traffic jam, an accident, or a sudden traffic speed decrease is very important to limit the number of accidents on the road.
On some highways, dedicated systems are in place for detecting some of these conditions, typically traffic jam conditions. These systems rely on different infrastructure means, such as speed sensors, video surveillance equipment, and information boards to announce abnormal traffic conditions. A problem is that such infrastructure means are expensive to deploy and to maintain. Furthermore such infrastructure means cannot react very quickly in response to sudden conditions, and they cannot react accurately to traffic conditions with a limited impact on the road.
Examples of traffic detection systems based on a fixed infrastructure are briefly described below.
U.S. Pat. No. 6,150,961 to Alewine et al., entitled “Automated traffic mapping,” discloses a system of mobile units installed in multiple vehicles in traffic. These mobile units include both wireless communications devices and apparatus that determine the location of each vehicle. Monitoring a vehicle's position as a function of time also reveals the velocity of the vehicle. Position and speed information is periodically broadcast by the vehicles to a central monitoring station and to neighboring vehicles. At the central monitoring station, the collective input of a set of vehicles is processed to provide an instant chart of traffic conditions in the area. Warnings of delays or updates on traffic conditions on the road ahead are then automatically returned to subscribers of the information or are used as part of an Intelligent Vehicle Highway System (IVHS). Neighboring vehicles within a region communicating with one another form a network in which the broadcast information is processed locally on the respective vehicles to estimate possible problems ahead and consider computing an alternate road and/or checking with the central monitoring station for more information. If out of range of the central monitoring station, the vehicles in the network form a local area network for the exchange and update of information, and when any vehicle in the network is within range of the central monitoring station, the local area network data is uploaded to help update the overall traffic information.
U.S. Pat. No. 6,862,500 to Tzamaloukas Assimakis, entitled “Methods for communicating between elements in a hierarchical floating car data network,” discloses participating vehicles and egress points which communicate with each other according to an infrastructure mode. Participating vehicles communicate with other participating vehicles according to an ad-hoc mode. In an infrastructure mode packet transmitting method for a participating vehicle, beacon service table packets, vehicle service table packets, or packet bursts are created and transmitted. In an infrastructure mode packet receiving method for a participating vehicle, beacon service table packets, vehicle service table packets, packet bursts, or negative acknowledgement packets are received. In an infrastructure mode packet transmitting method for an egress point, an enhanced beacon packet or a negative acknowledgement packet is created and transmitted. In an infrastructure mode packet receiving method for an egress point, beacon service table packets, vehicle service table packets, or packets bursts are received. In an ad-hoc mode packet transmitting method for a participating vehicle, beacon service table packets, vehicle service table packets, packet bursts, or positive acknowledgement packets are created and transmitted. In an ad-hoc mode packet receiving method for a participating vehicle, beacon service table packets, vehicle service table packets, packet bursts, or positive acknowledgement packets are received.
U.S. Pat. No. 6,092,020 to Fastenrath et al., entitled “Method and apparatus for obtaining traffic situation data,” discloses a method for obtaining data on the traffic situation in a road network, wherein a plurality of vehicles involved in road traffic (“floating cars”) and equipped with sensory analysis equipment for collecting traffic-relevant sensor data, which include at least one variable representing the current speed v(t) of a given vehicle, wirelessly transmit to a center at chronological intervals individual reports concerning the current traffic situation in the vicinity of the given vehicle determined on the basis of collected sensor data by a data processing device arranged in the vehicle. The individual reports, in addition to containing a classifying interpretation of the traffic situation carried out by the data processing device based on the collected speed variables, which interpretation encompasses at least the class of “traffic-related hold-up” (traffic jam), also contain, as part of the report, a confidence factor F, which represents a measure for the waviness of the chronological profile of the speed variables, especially the vehicle speed v(t), for the period of time to which the given individual report relates.
Some of the more recent systems are based on a GSM infrastructure. However, the GSM technology has a limited locating capacity and these systems require the presence of active GSM phones in vehicles. Other systems are based on the exchanged of traffic information between vehicles by means of wireless communications.
U.S. Pat. No. 5,428,544 to Shyu Jia-Ming, entitled “Traffic information inter-vehicle transference and navigation system,” discloses a method and an apparatus for the transference of traffic information among vehicles and for assisting navigation of the vehicles. The traffic information of the vehicles, such as the speed and the route and direction, is remotely transmitted to each other during passing, via communication devices mounted on each of the vehicles. The apparatus comprises sensors to detect the direction and the displacement of the vehicle; a microcomputer to recognize the position of the vehicle by referring the detected direction and displacement to a digitized map; a receiver to receive the passing vehicle's traffic information to be processed by the microcomputer; a transmitter to transmit the traffic information to the passing vehicle; and a navigation unit in the microcomputer to generate navigation information and indicate the traffic information of vehicles ahead is transmitted to a receiving vehicle in an indirect manner via a passing
International patent application WO04036815, entitled “Enhanced Mobile Communication Device and Transportation Application,” discloses an enhanced mobile communication device which communicates directly with other enhanced mobile communication devices in an ad-hoc mode over a wireless medium. The device transmits and receives packets of digital data. Network transmission parameters for transmitting the packets of digital data are dynamically customized according to the sender and receiver positions so as to increase the probability that the packets are received. Packet lengths may be varied. The number of times a packet is transmitted may also be varied according to activity in the wireless medium. Attempts to transmit are made periodically and the period of transmission is adjusted according to activity in the wireless medium. In a transportation application, the packets comprise vehicle traffic congestion update information. The device maintains a traffic database and a map database. Traffic congestion update information is exchanged with other devices. Routes through the map from a source or current position of the device to a destination are computed according to an analysis of the traffic database
U.S. Pat. No. 6,708,107 to Impson et al., entitled “Real-Time Ad Hoc Traffic Alert Distribution,” discloses a traffic characterization system and method of use for executing a traffic characterization protocol over an ad hoc communications network. Conventional in-vehicle computers and conventional wireless local area network (LAN) transceivers host the traffic characterization system and the messages generated by the system. As a traffic jam occurs, the mobile units send out traffic characterization data in a sequence activated by the content of the messages and traffic characterization protocol of the present invention. All vehicles participating in the traffic characterization system and approaching the traffic jammed area receive the characterization data and have the opportunity to route around the jam.
One of the problems of the systems disclosed in the prior art previously cited is that they are based either on a terrestrial infrastructure or on a specific communication network. These systems generally require a measure and exchange of a huge amount of information and the use of complex algorithms to characterize the traffic.